Toll-like receptors (TLRs) are present on many cells of the immune system and are involved in the innate immune response. In vertebrates, this family consists of eleven proteins called TLR1 to TLR11 that recognize pathogen associated molecular patterns from bacteria, fungi, parasites, and viruses. TLRs are a key mechanism by which vertebrates recognize and mount immune responses to foreign molecules and also provide a link between the innate and adaptive immune responses. Some TLRs are located on the cell surface to detect and initiate a response to extracellular pathogens and other TLRs are located inside the cell to detect and initiate a response to intracellular pathogens.
TLR9 recognizes unmethylated CpG motifs in bacterial DNA and in synthetic oligonucleotides. While agonists of TLR9, and other TLR agonists, can initiate anti-tumor immune responses, TLR agonists can also induce immune suppressive factors that may be counterproductive for effective tumor responses.
There is a need for cancer immunotherapies that induce antitumor responses, and keep the immune system productively engaged to improve the overall response.